[alsa-devel] Specs available for Sweex External 5.1 with digital in/out USB 2.0 / C-Media CM6207

Jon Smirl jonsmirl at gmail.com
Wed Jun 4 19:38:01 CEST 2008

On 6/3/08, Erik Slagter <erik at slagter.name> wrote:
> Hi there,
>  Today I bought this sound device, I was hoping it had the C-Media CM650?
> USB chip which is already supported by alsa (according to the list).
>  Instead it has a CM6207 inside.
>  The good news is that it supports USB audio "class" and it's more or less
> usable, some mixer outputs are available (although they're all called
> "speaker") and with some trickery the various outputs can be used.
>  The other good news is that Sweex supplies the "official" datasheet from
> C-media which I think is quite interesting and may very well be useful to
> resolve the last few issues.

Write this up for the Free Linux Driver project.


>  These are the actual issues (so far, I didn't yet test it exhaustively):
>   - using 2 channel output the sound is garbled; it looks like the "wrong" 2
> channel alt setting is used (output of /proc/asound/card?/stream0 on
> request), 4/6 channel output is OK though.
>   - some high squeeking noise although C-Media claims the IC to be high-end
> (or maybe their definition of high-end differs from mine ;-))
>   - all outputs are labelled "speaker 1"
>   - only two outputs have a mute knob, the others cannot be silenced in any
> way, only turned down
>   - one of the two outputs with the mute knob doesn't appear to do anything
> (or maybe it's the sp/dif output?)
>   - the other (with mute) controls the front output
>   - the others (without mute) don't seem to do anything at all
>  Is this a typical case of (a) bug(s) in the usb audio class driver or
> should I think of "vendor extensions" here?
>  Would any of the developers have some interest in the datasheet of the chip
> and or any data of this thing? Of course I'd like it very much if the device
> would be fully supported but I can only ask nicely ;-)
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Jon Smirl
jonsmirl at gmail.com

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